It's important not to overstate this, because a variety of factors are probably at play. But one big theory about why the rates of heroin relapse were so low on return to the U.S. has to do with the fact that the soldiers, after being treated for their physical addiction in Vietnam, returned to a place radically different from the environment where their addiction took hold of them.
"I think that most people accept that the change in the environment, and the fact that the addiction occurred in this exotic environment, you know, makes it plausible that the addiction rate would be that much lower," Nixon appointee Jerome Jaffe says.
Here is what happened in Vietnam: Soldiers spent all day surrounded by a certain environment. They were inundated with the stress of war. They built friendships with fellow soldiers who were heroin users. The end result was that soldiers were surrounded by an environment that had multiple stimuli driving them toward heroin use. It's not hard to imagine how living in a war zone with other heroin users could drive you to try it yourself.
Once each soldier returned to the United States, however, they found themselves in a completely different environment. Not only that, they found themselves in an environment devoid of the stimuli that triggered their heroin use in the first place. Without the stress, the fellow heroin users, and the environmental factors to trigger their addiction, many soldiers found it easier to quit.
